How to clean dark spots in elbows, knees, neck and genital area(legs area to be !

How to clean dark spots in elbows, knees, neck and genital area(legs area to be exact)?

I had gained weight over the years, but I finally lost some many pounds and my question is what can I do to clean black spot on my neck, armpits, and elbow ?what should I buy or is there any homemade product or solution to clean and make it go back to my skin color? I also gained black spot around both of my legs in between my genitals, what can I do to clean that, I shaved and it looks disgusting and is I guess a turn off for my girlfriend, what can I do that is not harmful in the area I am a white person and it looks not so good? Please help me? Or what sort of hygiene habit I need to get into to prevent this from happening?

You can try a skin bleaching or whitening system. They usually have them at department stores.